1. Field of the Invention
The present invention relates to a telephone subscriber station having a base set connected to the telephone network and a cordless hand set, having a first transmission segment which contains a first NF/PPM converter and a first IR pulse transmitter in the base set and, connected by way of a first optical transmission channel, a first IR pulse receiver and a first NF/PPM converter in the cordless hand set, and also having a second transmission path which contains a second NF/PPM converter and a second IR pulse transmitter in the cordless hand set and, connected via a second optical transmission channel, a second IR pulse receiver and a second PPM/NF converter in the base set, with a phase synchronization circuit in the base set and a call device in the hand set.
2. Description of the Prior Art
Such a telephone subscriber station is, in general, known in the art. Its manner of operation will be described below on the basis of FIGS. 1 and 2, in which FIG. 1 is a block diagram of a telephone subscriber station and FIG. 2 is a pulse diagram for the pulse phase modulation employed in the subscriber station.
The abbreviations employed herein are defined as:
PPM=Pulse phase modulation;
NF=Low frequency;
MFV=Multi-frequency method;
IWV=Pulse selection method; and
IR=Infrared.
The telephone subscriber station of FIG. 1 comprises a base set 1 and a cordless hand set 2.
The base set 1 comprises an IR pulse transmitter 4, an IR pulse receiver 8, a PPM/NF converter 19, and an NF/PPM converter 20, a sawtooth generator 21, a delay circuit 22, a power supply 24, and, optionally, the telephone apparatus 15 with a cord and a dialing structure 12.
The cordless hand set 2 contains an IR pulse transmitter 7, an IR pulse receiver 5, an NF/PPM converter 25, a PPM/NF converter 26, a sawtooth generator 27, a microphone 28, a telephone receiver 29, a calling or dialing structure 30 and a power supply 31.
When a speech signal arrives on the leads 23 of the subscriber line, the same is converted into PPM signals in the NF/PPM converter 20 and is emitted by way of the IR pulse transmitter 4 into the optical transmission channel 3. This signal is received in the IR pulse receiver 5 and is relayed by way of the PPM/NF converter 26 to the telephone receiver 29. A reply returns to the leads 23 of the subscriber line via the microphone 28, the NF/PPM converter 25, the IR pulse transmitter 7, the optical transmission channel 6, the IR pulse receiver 8 and the PPM/NF converter 19.
A dialing device can be located in the base set 1 and/or in the cordless hand set 2. The arrangement 30 in the cordless hand set 2 can be either a multi-frequency or dial pulse device. It it is only a matter of a call device, then the dialing of the telephone called party must be carried out by a person at the base set. If the arrangement 30, however, is a dialing (MF or dial pulse) device, then the called party can be directly dialed.
NF/PPM and PPM/NF converters are standard components. In the NF/PPM converter, pulses of identical size are diverted from the periodically returning neutral position in accordance with the amplitude of the NF signal. Thereby, the chronological deflection is proportional to the NF signal. The PPM/NF converter reconverts the phase fluctuations into voltage values, i.e. into the original NF signal. The NF/PPM and PPM/NF conversion expediently occurs with the assistance of a saw tooth generator.
The NF/PPM converter 25, as well as the PPM/NF converter 26 are driven from a common sawtooth generator 27, and the NF/PPM converter 20 as well as the PPM/NF converter 19 are driven by the common sawtooth generator 21. The synchronization of the sawtooth generator 21 with the sawtooth generator 27 occurs via the delay circuit 22.
FIG. 2 illustrates a pulse diagram for the PPM transmission between the hand set and the base set.
The sawtooth wave form c is generated by the free-running sawtooth generator 27 of the hand set, while the sawtooth wave form g is generated by the entrained sawtooth generator 21 of the base set. A sawtooth period of, for example, 125 .mu.s is divided into two channels K1 and K2. PPM pulses are transmitted from the handset to the base set in the channel K1 and PPM pulses are transmitted from the base set to the hand set in the channel K2. A PPM pulse a is transmitted by the IR pulse generator 7 of the hand set and, now referenced d, it is received by the IR pulse receiver 8 of the base set. The PPM pulse e is transmitted by the IR pulse transmitter 4 of the base set; this, now being referenced on the receiving side as b, and is received by the IR pulse receiver 5 of the handset. The shift of the PPM pulses amounts to approximately +30 .mu.s.
The transmission of special characters between the hand set and the base set has not yet been implemented in the art discussed above.